Electric clock



Jan. 25, 1944 T. B. GIBBS ET AL ELECTRIC CLOCK Filed Sept. 9, 1940INVENTQRS. Thomas 5. Gabbs Patented Jan. 25, 1944 ELECTRIC CLOCK ThomasB. Gibbs and Jean assignors to George W. cago, 111., a corporation ofDelaware Application September 9, 1940, Serial No. 355,952

Fink, Delavan. Wis.,

Borg Corporation, Chi- 19 Claims. (01. 58-28) The present inventionrelates in general to electric clocks, and more in particular to clocksof the type in which the mainspring is omitted and an electromagnet isemployed to maintain the balance in oscillating condition, the magnetbeing intermittently energized under control of the balance. Clocks ofthis type are well adapted for use in automobiles, and the object of theinven tion may therefore be considered to be the pro-- vision of a newand improved autombile clock, although certain features of the inventionare not necessarily so limited and are adapted for use in other types ofclocks.

A feature of the invention is a new and improved contact device forcontrolling the circuit of the drive magnet. A small permanent magnet isused, which actuates the contact device at each oscillation of thebalance.

A further feature is a new and improved magnetic circuit for the drivemagnet, so designed that the rate of the clock is substantiallyindependent of voltage variations over a range which is at least asgreat as that which is usually met with in practice.

A further feature is a new and improved drive mechanism by means ofwhich the oscillatory motion of the balance is converted into aunidirectional motion of the clock train.

A still further feature is a new and improved drive mechanism which alsofunctions as a contact device for controlling the circuit of the drivemagnet, thus permitting a separate contact device to be dispensed with.

There are other features which with those mentioned above will bedescribed in detail hereinafter, reference being had to the accompanyingdrawing, in which- Fig. l is a rear view of a clock constructed inaccordance with the invention;

Fig. 2 is another rear view of the clock, on a larger scale, and withthe back frame plate removed;

Fig. 3 is a side view looking toward the balance as seen in Fig. 2;

Fig. 4 is another side view taken from the as the clock is seen in Fig.3;

Fig. 5 is a fragmentary view showing details of the magnetic typecontact device for controlling the circuit of the drive magnet;

Figs. 6, '7 and 8 are diagrammatic views showing the essential parts ofthe new drive mechanism in different positions which they assume duringoscillation of the balance; and

Figs. 9 and 10 are fragmentary views showing left - as shown in Figs. 2,3, and 4.

how the drive mechanism can be used for controlling the magnet circuit.

Referring to the drawing, the various parts of the clock are mounted ona frame which comprises the front plate 2, the plate 3, and three posts5, 6, and I. The front plate 2 may be circular in shape, and has thethree posts secured to it by a riveting or staking operation, asindicated in Figs. 3 and 4 of the drawing. Each post is reduced indiameter for about half its length, as shown by the dotted lines, andthe ends of these reduced portions are threaded. The shape of the plate3 can be seen from Fig. 2, which indicates that in the vicinity of posts5 and 5 the plate conforms to the inner surface of the pole pieces l0and II, except fo the two cars 8 and 9, which'pass through slots if].the pole pieces and are drilled to receive the reduced portions of theposts. Plate 3 is also drilled at a point corresponding to the locationof post I.

In assembling the frame, the two pole pieces are forced onto the earsBand 9 of frame plate 3, where they are retained by the press fit. The.plate 3may then be placed in position against the shoulders on posts 5,6, and I, after which tubular spacers IZ are assembled on posts 6 and l,and a short spacer l3 on post 5. The contact springs I l and m, formedintegrally with one another, are then piaced on post 5 above spacer 13,after which the spacer I5 is added. The assembly is then securedtogether firmly by means of nuts It. It Will be understood that otherparts may also be mounted on plate 3 before it is assembled in me frameif desired.

The back plate 4 may be regarded as part of the frame, although it ISreadily removable. The plate 4 is prelerably made of some suitable sheetinsulat ng material. It has holes drilled to correspond to the locationsof posts 5, ii and l, andis clamped in position against the nuts lb bythree nuts I1. I

The balance comprises a ring I B, of brass or other suitable material,and a four-pole armature which also functions as a support for the ring.The armature is a sheet-metal stamping of high grade magnetic material,as will be subsequently explained more in detail, and is shaped The fourpoles are indicated at I9, 20, 2|, and 22, and are connected to acentral hub section by means of spokes 23 formed integrally therewith.The ends of the poles are bent at right a circle of the same diameter asference of ring l8, thus forming a partial enclothe" outline of sure forthe ring, which may be held in position by a press fit, or in anysuitable manner.

The balance is mounted on an arbor 25, which has a jeweled bearing atone end in the downturned portion 26 of frame plate 3, as shown in Figs.2 and 4. At the other end the arbor 25 has a plain jeweled bearing andalso a thrust bearing, which are supported on the balance cock 2! inknown manner. The thrust bearing is required because the clock isintended to be mounted with the balance arbor in a vertical position.The balance cock is provided with a base portion 28, which is secured tothe frame plate 2 by means of screw 29. It will be noticed that thebearings for the balance arbor are located so close to the frame plate 2that the rim of the balance projects slightly beyond the face of theplate, the latter having an opening therein, as shown in Fig. 2, inwhich the balance oscillates. The purpose of this construction is toenable the oscillating balance to be observed from the front of theclock, it being understood that the dial will be provided with a similaropening.

The usual hairspring is indicated at 39 and has one end secured to thebalance arbor and the other end secured to a stud 3| which projects fromthe base 28 of the balance cock. A regulating mechanism is alsoprovided, as shown, and includes a toothed sector 32 which is rotatablymounted on the balance cock in known manner. The sector 32 is in meshwith a gear 33 which is mounted on the under side of the plate 4 and maybe rotated by means of a pointer 34. These parts are of the usualconstruction and will require no extended description. It will sufflceto say that rotation of pointer 34 rotates the gear 33 and sector 32,and that the latter moves the regulator pins along the hairspring tochange the effective length thereof.

Mounted on the balance arbor, as shown in Fig. 2, there are a safetyroller 35 and a pinion 38 having a single tooth 31, whichcooperate,'respectively, with the safety wheel 38 and the lever 39. Thesafety wheel 38 is mounted on an arbor 40, which has a bearing at oneend in the post I. At the other end, the arbor 46 has a bearing in themember 4|, which forms part of a bracket including the base 42.Thebracket is secured to the frame plate 2 by means of a screw 43. Thearbor 49 drives the clock movement by means of the worm 44 and a gear inmesh therewith which is mounted on the shaft 45. The rest of the geartrain may be of known construction and has been omitted in order toavoid confusing the drawing.

The lever 39 is pivotally mounted on a stud 41 which is secured to thebracket 4|. The lever is adapted to be rotated on its pivot by the tooth31 of pinion 36 during the oscillatory motion of the balance, and isrestored to normal each time by the spring 14 which bears on the twoprojections .48 and 49. Spring l4 may be formed integrally with springl4. At the end of the lever 39 there is a pin 50, which cooperates withthe teeth of the safety wheel 38 in a manner which will be explained.

Attention may now be directed to the construction of the electromagnetwhich drives the balance. This magnet comprises the two pole pieces iand H previously referred to, which terminate in poles 55 and 56, andwhich are connected to opposite ends of the core 51. The core is formedwith a shoulder at each end and the pole pieces are clamped against theshoulders by means of nuts, as shown clearly in Figs. 2 and 4. Themagnet winding is indicated at 58. Associated with the electromagnetthere is a condenser 59. The electrical connections for these parts willbe described shortly.

The contact device for controlling the electromagnet is best seen inFig. 5. As previously explained, the double contact spring, comprisingspring 14 and i4, is clamped between the spacers l3 and I5 on the framepost 5. Spring 14 cooperates with a fixed contact member 63, which isclamped to the frame plate 3 by means of a screw 65 and nut 69. Aterminal member 64, best seen in Fig. 2, is assembled just above thecontact member 63, and these parts, as well as the screw 65, areinsulated from the frame plate 3 by means of insulators 66, 61, and 68.It will be understood also that the members 63 and 64 have openingstherein which are large enough to avoid contact with screw 65.

The contact spring 14 is tensioned in an up ward direction, as seen inFig. 5, so that it tends to break contact with the contact member 63.The spring is operated to close the contact by means of an armature 62,secured to the spring, and a small permanent magnet 69, which is mountedon the balance arbor. The magnet 60 is preferably of Alnico and has anopening in which there is fitted a bushing 6|, which has a press fit onthe arbor 25. The poles of the magnet are at the opposite ends thereof,and the magnet is eccentrically mounted on the arbor so that during theoscillation of the balance one of the poles comes much closer to thearmature 62 than the other pole. The distances are so proportionedto'the strength of the magnet that the armature can be attracted only bythe pole which comes the closest to it. The drawing Fig. 5 shows thearmature 62 in attracted position, the contact between spring i4 andcontact member 63 being closed. When the arbor 25 and magnet 60 arerotated in either direction, the armature is released and the contact isopened. Rotation of the magnet through degrees will not close thecontact because the pole at the rounded. end of the magnet passes thearmature at too great a distance for it to be operatively attracted.

The magnet 66 is so located as regards its angular position on the arborthat a line passing centrally through the poles of the magnet and thearbor will bisect the angle formed by the spokes 23 which support thepoles l9 and 20 of the balance armature. This relation can be seen fromFig. 3, which also shows that when the balance is symmetrically locatedwith respect to the poles 55 and 56, with pole 56 midway between thearmature poles I9 and 22, the operative pole 3; magnet 60 is inalignment with the armature The circuit connections for theelectromagnet 58 may now be described. The condenser 59 may be providedwith heavy terminal conductors Ill and H, as seen in Fig. 2. Theconductor 16 is formed as shown in the drawing, and its end is solderedto the terminal member 64. The conductor H is bent down around the edgeof the frame plate 3 and extends along the under side of the frame plateto the screw 65, where the end of the conductor may be formed in aloop.-

as shown in Fig. 5, and secured under the head of the screw, a suitablewasher being interposed if desired. The ends of the winding 58 arebrought out at opposite ends of the coil by way of conductors I2 and i3,which are soldered to conductors and II, respectively. It will beunderstood, therefore, that the condenser 59 and winding 58 areconnected in parallel; that is, the condenser is bridged around themagnet winding.

There is a binding post 81 mounted on the frame plate 4, which isprovided with a spring clip 88 beneath the frame plate. This clippresses against the end of the screw 65, as seen in Fig. 3. Assumingthat the clock is used in an automobile, the ungrounded pole of thestorage battery is connected to the binding post. With the batteryconnected in this manner, the complete circuit for the electromagnet maybe traced from the ungrounded pole of the battery by way of binding.post 81, spring clip 88, screw 65, conductor ll, conductor I3, winding58, conductor 72, conductor I8, terminal member 64, contact member 63,and spring 14 (armature 62 being in attracted position) to the frame.Since the frame of the clock is grounded on the car, the circuit iscompleted by way of the chassis of the car to the grounded pole of thebattery. It will be clear that this circuit is closed intermittentlydunng oscillation of the balance by means of the magnet 60, armature 62,and spring I4.

The circuit arrangements described are capable of various modifications.A non-grounded circuit can be used if desired, and may be necessaryunder some conditions. In order to keep the circuit clear of the frame,the contact spring i4 is made separate from spring 14' and is suitablyinsulated at the fixed end where it is clamped between the spacers l3and I5. A terminal member similar to 64 may be assembled next to thespring I4 to provide for the convenient attachment of a conductor.

The construction of the clock and the various parts thereof having beendescribed, considei'ation may be given to the operation, with specialattention to the novel features provided by the invention.

The hairspring 30 is so assembled and adjusted with respect to thebalance that when the battery is disconnected the hairspring will tendto return the balance to the position in which it is shown in Fig. 3. Inthis position the poles 55 and 56 of the electromagnet are midwaybetween the adjacent armatures poles on the balance, and the operativepole of magnet 60 is adjacent the armature 62. The adjustment of thehairspring is not at all critical, since the attraction between themagnet 60 and armature 62 will rotate the balance to the position inwhich it is shown, provided the hairspring adjustment is evenapproximately correct. In other words, the magnet 68 will pull itselfin, if brought within range of the armature 62 by the hairspring, andwill maintain the circuit of the electromagnet 58 closed at contactspring l4. This feature presents a decided advantage over the usual typeof contact arrangement in which the hairspring alone is depended on tomaintain the contact closed when the battery is disconnected.

When the battery is connected, a flow of current over the previouslytraced circuit is established and the electromagnet 58 is energized. Theresulting magnetic field passes through the armature and the balance isthus placed in a condition of unstable equilibrium. The rotative forcestending to rotate the balance in opposite directions will not be exactlyequal, for obvious reasons, and the balance will start to rotate in onedirection or the other. As soon as the rota- 36 and the direction of therotation is shortly reversed, with the result that the circuit of theelectromagnet is again closed when the magnet 68 comes within operatingdistance of the armature 62. Thus the balance is given another rotativeimpulse. but in the opposite direction The operation continues in thismanner and in a very short time the balance will attain its normalamplitude, a power impulse being received during each oscillation orbeat, when the operative pole of magnet 60 passes the armature 62.

The oscillation of the balance drives the clock movement through themedium of the lever 39 and the safety wheel 38, the latter being fixedto the arbor 40 carrying the 'worm 44, which is the first element of thegear train. The manner in which the drive operates can best be explainedin connection with Figs. 6, 'I, and 8, which show the essential parts ona larger scale and with the view unobstructed by other parts.

It may be assumed that the balance arbor 26, safety roller 35 and pinion36 are rotating in the direction shown by the arrow toward the positionin which these parts are shown in Fig. 6. As the rotation continues, thenotch in the safety roller 35 will pass the tooth 8| of the safety wheel38 without engaging the said tooth, for there is no rotative force beingapplied to the safety wheel. When the parts reach the position in whichthey appear in Fig. 6, the tooth 31 of pinion 36 engages the end oflever 39 and, as the rotation of the pinion continues, rotates the leverin aclockwise direction on its pivot 41 far enough to permit the piniontooth to pass by. The lever is rotated against the tension of spring 14and is instantly restored to normal as soon as it is released by thepinion tooth.

The balance and associated parts continue to rotate in the directionindicated in Fig. 6 until stopped by tensioning of the hairspring,whereupon the direction .of rotation is reversed, and these parts,including the safety roller 35 and pinion 36, start rotating in thedirection shown by the arrow in Fig. 7. When the pinion 36 reaches theposition in which it is shown in Fig. 7, the tooth 31 comes intoengagement with the end of lever 39, and the lever is rotated on itspivot 41 as the pinion tooth passes by. In the normal position of thelever pin 50 is just outside the circle defined .by the extremities ofthe teeth of wheel 38, but when the lever is rotated in acounterclockwise direction the pin crosses the circle and engages tooth83, thereby starting the rotation of wheel 38. The safety roller 35 isso positioned on arbor, 25 with respect to pinion 36 that the notch inthe safety roller arrives at the tooth 82 just as the lever 39 startsthe rotation of wheel 38. The tooth 82 is therefore caused to enter thenotch in the safety roller by the further rotation of wheel 38.

As the parts reach the position last described, the lever 39 is releasedby tooth 3'! and is instantly restored to its normal position. Thesafety roller 35 now carries on with the rotation of wheel 38 andcompletes its rotation through the angular distance of one tooth, thetooth 84 and the wheel is locked against overrun by the engagement oftooth 85 with the periphery of the safety roller.

The operations just described are repeated during the next two beats ofthe balance and continue in the same manner. It will :be appreciatedthat since the safety wheel 38 is fixed on the arbor 40, each rotativemovement of the safety wheel will advance the clock movement. It will beclear also that the safety wheel is rotated only during alternate beatsof the balance, when the balance and associated parts are moving in aclockwise direction, as seen in Figs. '7 and 8, the operations of thelever 39 which take place during those beats in which the balance ismoving in a counterclockwise direction being ineffective. Thus the clockmovement is always driven in a forward direction by the oscillation ofthe balance.

It will be desirable now to consider the operation of the electromagnetand the control of the electromagnet circuit somewhat more in detail.Assuming that the :balance and magnet 60 are rotating in a clockwisedirection as seen in Figs. 3 and 5, the magnet 60 is able to operativelyattract the armature 62 before coming to exact alignment therewith, andaccordingly the electromagnet circuit is closed by spring l4 shortlybefore magnet 60 reaches the position in which it is shown in Fig. 5,even though sometime is required for the operation of armature 62. Whenthe circuit is closed, therefore, the armature poles l9 and 2|, throughthe medium of which the next rotative impulse is to be given to thebalance, are farther from the electromagnet poles 56 and 55 than are thearmature poles 22 and 20; in fact, at the time the circuit is closed thepoles 22 and 20 may not be entirely out from between poles 56 and 55.The building-up of the magnetic field is delayed, however, due to theinductance of the magnet winding and also due to the momentaryshort-circuiting effect of condenser 59, which charges when the circuitis closed, so that by the time an appreciable amount of flux begins topass through the armature it has reached approximately the position ofFig. 3. As the armature advances from this position, the poles l9 and 2|approach and begin to enter between the electromagnet poles 56 and 55,with the result that the energization of the electromagnet applies astrong rotative force or torque to the balance.

The magnet 60 releases armature 62 and opens the circuit at a time whenthe armature poles I6 and 20 have entered about halfway, more or less,between the magnet poles 56 and 55. The release is delayed somewhat dueto the increased pull between the magnet and armature when the latter isin operated position. When the circuit is broken, the inductance of theelectromagnet winding tends to maintain the current fiow, in which it isaided by the discharge of the condenser, with the result that theenergization of the electromagnet is prolonged for an appreciable lengthof time during which it continues to apply a driving torque to thebalance.

From the foregoing, it will be seen that an eflective driving torque isapplied to the balance, notwithstanding the completely symmetricalarrangement of the magnet 60, balance armature poles, and electromagnetpoles, which offhand might lead one to believe that substantially equaland opposite rotative forces would be applied to the balance. That suchis not the case is due to the several factors discussed. Although theelectromagnet circuit may be closed in advance of dead center (theposition in which the parts are shown in Fig. 3), the opening of thecircuit is delayed for more than an equivalent amount; that is, theopening of the circuit occurs at an angle past dead center which isconsiderably greater than the angle of advance. When the circuit isclosed, the building-up of the magnetic neld'is delayed, and when thecircuit is broken the decay of the field is also delayed, for reasonsexplained. All these factors cause an effective magnetic field to beestablished and maintained over a time interval which substantiallycoincides with the time interval during which the poles I9 and 2| aremoving into alignment with the field poles from the position in whichthese parts are shown in Fig. 3, a time interval during which theattraction of the field poles for the armature poles l9 and 2| isincreasingly preponderant over their attraction for armature poles 22and 20. Thus the balance is given a strong rotative impulse in thedirection in which it is assumed to be moving, that is, in clockwisedirection.

When the balance reverses its direction of rotation, the same operationsoccur as have been described in detail above. The various factorsdiscussed cause the establishment and disestablishment of the field tobe delayed with respect to the motion of the balance, but since thebalance is rotating in the opposite direction the field is effective ata time when the armature poles 22 and 20 are operatively related to thefield poles. Thus the balance is given a rotative impulse in a counterclockwise direction.

The condenser 59 plays an important part in the operations justdescribed. In addition to its function of preventing arcing at thecontact when the circuit is broken, the condenser receives energy fromthe battery when the circuit is closed, which it delivers to theelectromagnet when the circuit is opened, and thus provides for a morepowerful energization of the electromagnet than could otherwise beobtained during the short time in which the circuit is closed. Thecondenser should preferably be of the electrolytic type in order toobtain a fairly high capacity within the size limits which are imposedby the dimensions of the other parts of the clock.

When the clock described herein is used in an automobile it is subjectedto variations in voltage, which ordinarily would have a considerableerrect on the rate of the clock. While the normal voltage is about 6volts, it may drop as low as 4 volts or even less on starting and riseto 7.5 volts -or thereabouts when the battery is charging.

These varying voltages tend to afiect the rate of the clock by varyingthe amplitude of the balance. That a considerable eifect on theamplitude is produced may be appreciated from a consideration of thefact that with a given load the power delivered varies as the square ofthe voltage. Thus with an automobile clock, it the voltage is raisedfrom 4 volts to 8 volts, or doubled, the power delivered is quadrupled,unless some means is employed to prevent it.

For the best results as regards accuracy in the rate, it is desirablethat the balance should have an amplitude of about one and three-eighth:

turns. This value oi! amplitude may be considered to be the approximateoptimum, from which a variation of about one quarter turn above or belowmay be permitted without appreciably affooting the rate. We havediscovered that by properly designing the magnetic circuit the powerdelivered to the balance may be maintained constant enough to keep thebalance oscillating within the permissible range, with the voltagevariation of from 4 volts or slightly less to over 7.5 volts. The mannerin which this is done will now be explained.

The amplitude of the balance is a function of the power delivered to itby the armature and the stillness of the hairspring. The power that thearmature can deliver depends on the amount of flux it can carry when theelectromagnet is energized, which in turn depends on the crosssection ofthe magnetic path through the armature. The armature poles preferablyshould have a certain minimum width circumferentially or the balance inorder to properly distribute themagnetic pull during the motion of thebalance, and hence at the poles the cross-section of the magneticcircuit is necessarily more or less fixed, but at points between thepoles it can be varied within rather wide limits. As a firstconsideration, therefore, the cross-section of the poleconnecting spokessuch as 23 (see Fig. 3) is so proportioned to the strength of thehairspring that when the spokes are substantially saturated the powerdelivered will be sufiicient to produce oscillations of the desiredamplitude. The electromagnet is then designed so that at a minimumenergizing voltage, say 4 volts or somewhat less, it will produce therequisite saturating flux for the armature.

It will be understood that the values of the factors under discussion atthis point canbe varied considerably, so long as the correct proportionsare substantially maintained. The stiffness of the hairspring and thepower delivered by the armature when saturated (as determined by thecross-section of the magnetic clrcuit between the poles) should be sorelated that the correct amplitude is obtained, and the electromagnetshould be capable of delivering the necessary saturating flux at theminimum operating voltage. The power of the electromagnet at the minimumvoltage should not greatly exceed this requirement. The requirement asto the' relation between the stiffness of the hairspring and thesaturation flux in the armature will in general make it necessary to usespokes 23 of considerably less width than the best pole width, as shownin the drawings, particularly Fig. 3, from which it can be seen that thespokes 23 have a width of about one-third the width of the poles such asl9.

The variation in balance amplitude in response to voltage variations isgreatly reduced by adherence to the foregoing principles, but this doesnot entirely solve the problem due to considerations which will bepointed out. As the voltage rises the flux passing through the armaturepoles is not strictly limited to the amount of flux that can be carriedby the spokes, but includes the leakage fiux between poles, which issufficiently great so that the total flux rises considerably faster thanthe magnetization curve of the spokes alone. It is desirable thereforeto limit, insofar as possible, the amount of flux that can be deliveredto the armature poles by the pole pieces of the electromagnet. Thisresult can be obtained in a satisfactory manner by reducing thecross-section of the pole pieces i ii and ii throughout a portion 01their length. The pole pieces could be of reduced cross-sectionthroughout, but it is desirable to have the poles 55 and 56 ofapproximately the same width as the armature poles, and the pole pieceshave to be of sturdy construction between the poles and points beyondthe posts 5 and 6 for obvious mechanical reasons. The reduction incross-sec tion is limited, therefore, to the portions of the pole pieceswhich extend between the posts and the magnet core, as illustrated inFig. 4 in the case of pole piece I0. I

As can be seen from the drawing, that portion of the pole piece illwhich extends from the vertical portion which is secured to the core tothe portion which is slotted to receive the ear 8 is greatly reduced inwidth, and'forms a section of reduced crosssectlon which tends to limitthe amount of flux that can be delivered to the pole 55. A certainsmallamount of leakage flux will by-pass this reduced section at highvoltages, but it is very effective nevertheless, and the wholearrangement produces very satisfactory results. Taking into account theleakage flux, the pole pieces l0 and II should be so dimensioned thatthe portions thereof which are reduced in cross section will carrysomewhat less flux than the spokes of the armature, which generallyrequires that the pole pieces have a smaller cross-section in thereduced portions than the cross-section of the armature spokes. Therequired cross-section depends on several factors, however, such as thestrength of the eleotromagnet and the material of which the pole piecesare constructed and can be determined by trial within the principlesexplained.

The selection of the proper magnetic materials for the balance armatureand the pole pieces is of importance for the best results. For thebalance armature nickel iron alloys, such as Allegheny metal, .Mu metal,or Permalloy, are desirable, as these materials have high permeabilityat low flux densities and have magnetization curves which are quite flatabove the knee. as contrasted with the magnetization curves of othermagnetic materials which show a more gradual increase in flux over awide range of increasing magnetization forces. The armature is operatedjust above the knee of the curve, where it is substantially flat overthe range of voltages which is met with in practice.

The nickel iron alloys mentioned above are also suitable for the polepieces and magnet core, but a less expensive material such as Armco ironcan also be used with good results. A pure soft ir'on such as Armco ironis all right for the field; but in the case of the armature, whereconsiderable stifiness and rigidity are required, thenickel iron alloysare more suitable.

As previously intimated, very excellent accuracy is obtained in a clockof this type by means of the armature and field construction described.Magnetization curves for the armature, which have been made under testconditions, show a flat top characteristic over the voltage range 4-8volts, which is much superior as regards low change in flux over theoperative voltage range to that exhibited by the magnetization curve ofany known material. This result is due to the use of the proper materialin the armature, in the first place, and to the advantage which issecured by the limitation as to the amount of flux that can be deliveredto the armature by the field. The total armature flux therefore remainsnearly constant when the clock is operating on different voltages withinthe specified range and the amplitude of the balance is not subject tovariations which would deleteriously affect the accuracy of the clock.

Attention may now be directed to the modifica tion shown in Figs. 9 and10, in which the drive mechanism is made to perform the function of acontact device for controlling the circuit of the drive magnet.

When this modification is used the springs M and i4, contact member 63,and the magnet 6!! are omitted. In placeof contact member 63, a spring94 is provided, which functions as a restoring spring for the lever 39.The lever is insulated from the frame in any suitable manner, as shownin Fig. 10, for example, where the lever is pivoted on the shoulderscrew 90. This screw is insulated from the bracket M by means of abushing 92 and washer 93, and is secured to the bracket by a nut a l.

The circuit of the magnet extends from the binding post 8'! by way ofspring clip 88, screw 65, conductors ii and is, winding of magnet 58,conductors l2 and i0, terminal member 64, spring 94, lever 39, tooth 31,pinion 36, and thence to the frame through the balance arbor andhairspring. This circuit is closed and opened by the engagement anddisengagement of lever 39 by the tooth iii of the pinion 35. Theseparts, or at least their contact surfaces, should be made of somenon-corrosive metal.

The hairsprlng normally tends to return the balance to the position inwhich it is shown in Fig. 3, and the parts of the drive mechanism are soadjusted that when the balance is in this position the radius of thetooth 3? will coincide with a line connecting the center of arbor 25with the center of the shoulder screw on which lever 39 is pivoted. Theend of lever 39 also lies in this line and when the battery isdisconnected, therefore, the tooth ill will engage the end of the leveron one side or the other, and the circuit of the magnet will be closedinside the clock. This position of the parts is illustrated in Fig. 9.The tooth 31 is in engagement with the end of lever 39, and the tensionof the hairspring tending to rotate the balance to the position of Fig.3 is opposed by the tension of spring 94 which tends to prevent therotation of the lever from its normal position. In equilibrium the leveris slightly out of normal position, while the rotation of the balance isarrested slightly short of its Fig. 3 position.

When the battery is connected, the drive magnet as is energized and animpulse will be applied to the balancetending to rotate it in aclockwise direction as seen in Fig. 3. since the armature poles is andiii are closer to the magnet poles Elli and 55 than the armature poles22 and 2!]. The rotation of the balance in a clockwise direction breaksthe circuit of the magnet, but it stores up tension in the hairspringand the direction of rotation is shortly reversed, with the result thatthe circuit is again closed. This time tension in the hairspring will beaided by the inertia of the balance, which will carry the balance pastdead center and the impulse resulting from the closure of the circuitwill be effective to continue the rotation of the balance in the samedirection. The circuit is broken when the lever is released by tooth 3?.The balance continues its rotation until the motion is arrested by thehairspring, whereupon the direction of motion is reversed and thecircuit is again closed, giving another operative impulse to thebalance. Thus the normal oscillating motion of the balance is quicklyestablished.

When the clock is running, the circuit of the drive magnet is closedeach time by the engagement of the tooth 31 with the end of lever 35 asdescribed, and during each oscillation or beat in a counterclockwisedirection the circuit is also broken at the same point. During each beatin a clockwise direction, however, the circuit is actually broken whenthe pin 50 disengages from a tooth of the wheel 38 just'after the leveris re leased by the tooth 31 of the pinion. That this is true will beevident from the fact that the wheel 38 and arbor 40 afford analternative circuit path to the frame of the clock. The pin 50 and thewheel 38 should also be made of some satisfactory contact materialtherefore.

If it is desired to confine the circuit control to the make and breakbetween the lever and pinion tooth, this result can be readily securedby insulating the pin 50 from the lever 39.

It will be seen from the foregoing that the invention provides animproved electric clock having a number of features which tend toenhance the utility of a device of this character. While the inventionhas been described in considerable detail, this has been done forconvenience in explaining the principles employed and to facilitate aclear understanding of suitable means by which the invention may becarried out in practice, but without any intention to limit theinvention to the specific construction shown and described.Modifications may be made within the principles of the invention, and Wedo not wish to be restricted, therefore, to the exact structuredescribed, but desire to include and have protected by letters patentall forms and adaptations of the invention which come within the scopeof the appended claims.

We claim:

1. In a clock, a balance, an electromagnet for driving said balance, acircuit for said electromagnet including a switch having a fixedcontact, a magnetic device for operating said switch, said devicecomprising an armature operatively associated with the switch and apermanent magnet oscillating with the balance, and means including saidfixed contact for limiting the movement of said armature under theinfluence of said magnet sufliciently to'prevent said armature fromengaging said magnet.

2. In a clock, a balance, an electromagnet for driving said balance, apermanent magnet mounted on the balance arbor and having one pole at agreater distance from th arbor than the other pole, an armature locatedadjacent the path of the remote pole and adapted to be op-- eratedthereby but not by the other pole, a switch operated by said armature,and a circuit for said electromagnet controlled by said switch.

3. In a clock, an oscillating system including an armature, anelectromagnet associated with said armature for supplying power tooperate said oscillating system, a hair-spring forming part of saidoscillating system and adapted to maintain said armature approximatelyin a predetermined position relative to the poles of said electromagnetwhen the clock is not running, means including a permanent magnet formoving said armature exactly to said predetermined position, a circuitfor said electromagnet, and a switch operated by said permanent magnetin said position to render said circuit effective, whereby said clock isable to start when current is supplied to said circuit, said switchincluding two contact members both mounted independent of the balancearbor.

4. In a clock, an electromagnetically driven balance, a toothed wheelfor driving the clock train, a pivoted lever actuated during alternatebeats of the balance to start the rotation of said wheel, and meanssupported on the balance for completing the rotation of said wheelthrough an angular distance of one tooth each time its rotation isstarted by said lever.

5.111 a clock, an electromagnetically driven balance, atoothed Wheel fordriving the clock train, a pivoted lever, means supported on the balancearbor for oscillating said lever on its pivot responsive to oscillationof the balance, means carried by said lever for starting the rotation ofsaid wheel when the lever moves in one direction on its pivot, and meanssupported on the balance arbor for completing the rotation of said wheelthrough an angular distance of one tooth each time its rotation isstarted.

6. In a clock, an electromagnetically driven balance, a toothed wheelfor driving the clock train, a pivoted lever, means rotating with thebalance for moving said lever on its pivot dur ing each beat of thebalance, and additional means rotating with the balance and cooperatingwith said wheel and with said lever for rotating said wheel duringalternate beats of the balance only.

'7. In a clock, an electromagnetically driven balance, a locking rollermounted on the balance arbor and having a single notch therein, a Wheelcoupled with the clock train and having teeth cooperating with saidroller, a pivoted lever adapted to advance said wheel to cause a tooththereof to enter the notch in said roller, and means rotating with saidbalance for actuating said lever.

8. In a clock, a balance, an electromagnet for driving said balance, atoothed wheel for driving the clock train, means supported on thebalance arbor for advancing said wheel, an actuating member supported onthe balance arbor, a pivoted lever operated by said member to rendersaid means effective during alternate beats of the balance, and acircuit for said magnet including said lever and actuating member.

9. In a clock, a balance, an electromagnet for driving said balance, atoothed wheel for driving the clock train, a pivoted lever. a member supported on the balance arbor for oscillating said lever, means includingsaid lever for advancing said wheel, and a circuit for said magnetincluding said lever and said member.

10. In a clock, means for driving the balance comprising an armature onthe balance arbor and an electromagnet, the magnetic circuit throughsaid armature including a portion the cross-section of which is sorelated to the stiffness of the hairspring that when the armature issubstantially saturated sufficient power will be delivered to thearmature to give the balance the desired amplitude, and pole pieces forsaid electromagnet including portions of such reduced cross-section asto substantially prevent the electromagnet from supplying flux to thearmature in excess of the amount required for saturation thereof.

11. In a clock, an armature for driving the balance, said armaturehaving its carrying capacity for magnetic flux related to the stiffnessof the halrspring that at approximate saturation values of flux thearmature will develop sufficient power to oscillate the balance at thedesired amplitude, an electromagnet for producing flux in said armature,and field members included in the magnetic circuit adapted to preventdelivery of excess flux to the armature in case the electromagnet isenergized at a higher voltage than that which is required in order toproduce approximate saturating flux in the armature.

12. In a clock, means for driving the balance comprising an armature onthe balance arbor and an electromagnet, a Winding for the magnet-'adapted to be energized at different voltages, a .member forming partof the armature and having such a restricted cross-section that itbecomes saturated at the minimum voltage, and members forming part ofthe magnet core and including sections of such limited cross-section asto substantially prevent delivery of excess flux to the armature whenthe electromagnet is energized at higher voltages.

13. In a clock, means for driving the balance comprising an armature onthe balance arbor and an electromagnet, a winding for the electromagnetadapted to be energized at diiferent voltages, and a magnetic circuitincluding an armature section and a magnet section which are of suchlimited cross-section that they become substantially saturated when thesaid winding is energized at a predetermined mini mum voltage.

14. In a clock, an armature mounted on the balance arbor, said armaturehaving poles con ected by a member of limited cross-section less thanthat of the poles, a magnet core having extensions terminating in polesadapted to cooperate with said armature poles, each of said extensionsincluding a portion adjacent the core whi h has a limited cross-sectionless than that -of the magnet poles, and a winding on said core sodesigned that when the winding is energized at a predetermined minimumvoltage the armature member and extension Dnlfiions of limitedCross-section will be substantially saturated.

15. In a clock, an electromagnet for driving the clock, an armature forsaid magnet mounted on the balance arbor, poles for said magnet andarmature, a magnetic circuit including a magnet section and an armaturesection and air gaps at said poles, said sections each including aportion having a smaller cross-section than the portions adjacent saidpoles, and a winding forming part of said electromagnet and so designedthat when energized at a predetermined minimum voltage the said portionsof the magnetic circuit of smaller cross-section will be substantiallysaturated.

16. In a self-starting electrical clock having a frame, a balance, anelectromagnet for drlving said balance, a circuit for saidelectiomagnet, a switch for controlling the said circuit, said switchincluding two contact members both mounted on the clock frame, a hairspring adjusted to bring the balance to rest in a predetermined angularposition when the current supply to the electromagnet is cut off, andmeans responsive to movement of the balance to said predeterminedposition to apply power independent of said hairspring to operate saidswitch and hold the same operated while the balance remains in saidposition.

17. In a clock, an oscillatory balance having an arbor, anelectromagnet, for driving said balance, a movable contact. an armaturefor moving said contact, a permanent magnet mounted on the balance arborand adapted to attract said armature on each oscillation of the balance,a stationary contact engaged by said movable contact when the latter ismoved by said armature, the entire movement of said movable contactbeing produced by said permanent magnet, said stationary contact beingso located that the movement of the movable contact and armature isarrested before the armature can engage the permanent magnet, and acircuit for said electromagnet controlled by said movable and stationarycontacts.

18. In a clock having a frame, a balance having an arbor, meansincluding a hairspring and an electromagnet for oscillating saidbalance, a circuit for said electromagnet, and means for controllingsaid circuit without physical engagement between any part mounted on theclock frame and any part mounted on the balance arbor, wherebymechanical interference with the motion of the balance is avoided, saidcontrolling means comprising a switch mounted on the clock frame and amagnetic device ineluding a part operatively associated with said switchand a part mounted on the balance arbor and effective at eachoscillation of the balance to operate said switch solely by theattraction through space between said parts.

19. In a self-starting clock having a frame, a balance having an arbor,a hairspring, an electromagnet cooperating with said hairspring to causesaid balance to oscillate in both directions from a central position, apermanent magnet mounted on the balance arbor, an armature supported onthe clock frame in such angular position around the balance arbor thatthe attraction between the magnet and armature is a maximum when thebalance is in said central position, whereby the mutual attractionbetween said magnet and armature aligns the balance in said centralposition when the clock stops and moves the armature toward the magnet,a switch operated by said armature and adapted to arrest the movementthereof before it engages said magnet, and a circuit for saidelectromagnet controlled by said switch.

THOMAS B. GIBBS. JEAN FINK.

